This application relates to mobile communication systems and in particular to television broadcasting in such communication systems.
“Broadcast-like” television (TV) services, which is to say, services with a conventional-television-channel concept, are already available for some mobile telephony networks. For example, the Mobile TV service of Telecom Italia Mobile (TIM) provides TIM subscribers with streaming content, enabling subscribers to watch TV shows on their mobile phones via GSM's general packet radio service (GPRS) technology. Another example is sports-team goal notification services, such as that provided by Vodafone, which uses GSM's multimedia messaging service (MMS). These current implementations are based on real-time streaming over unicast GPRS bearers, but capacity limits on application servers and core and radio access networks constrain service expansion and build-out. A few network operators currently deliver broadcast-like services in wideband code division multiple access (WCDMA) communication systems by circuit-switched (CS) streaming.
A multimedia broadcast/multicast service (MBMS) in GSM and WCDMA communication systems is currently standardized by the Third Generation Partnership Project (3GPP) in Technical Specification (TS) 23.246 “Multimedia Broadcast/Multicast Service (MBMS); Architecture and functional description”, V6.6.0, Rel. 6 (March 2003). According to the specification, MBMS is a point-to-multipoint service, in which data is transmitted from a single source entity to multiple recipients. Transmitting the same data to multiple recipients allows network resources to be shared, and the MBMS bearer service has broadcast and multicast modes. With MBMS, a complete set of multicast and broadcast services can be offered in telecommunication systems, such as UMTS and mobile telephony systems according to the GSM, Enhanced Data Rates for GSM Evolution (EDGE), and WCDMA specifications. The GSM EDGE radio access network is usually abbreviated as GERAN. Changes to network architecture as well as additional service-related signaling will be introduced to the existing systems by deployment of MBMS. Aspects of MBMS are described in M. Bakhuizen et al., “Mobile Broadcast/Multicast in Mobile Networks”, Ericsson Review vol. 82, no. 1, pp. 6-13 (2005).
Audio and video coder/decoders (codecs) used for streaming sessions for the small display screens typical of handheld devices are improving and are standardized by the 3GPP, e.g., TS 26.234 “Transparent end-to-end Packet-switched Streaming Service (PSS); Protocols and codecs”, V6.3.0, Rel. 6 (March 2003). Current implementations like the TIM Mobile TV service use streams that have data rates of 28 kilobits per second (kbps), but for very high quality content, the data rate needed is probably more than 100 kbps. For an intermediate level of quality, a data rate of 40-64 kbps is needed for a stream comprising both audio and video. For example, 12 kbps could be used for stereo audio encoded according to an adaptive multi-rate wideband codec (AMR-WB+) and 32 kbps for video encoded according to an MPEG-4 codec. Considering user sensitivity to errors in such streams, a block error rate (BLER) of 1%-2% or less may be needed for acceptable performance.
Another ongoing standardization activity is the Digital Video Broadcasting (DVB) Project, which aims at including DVB receivers in mobile terminals, such as mobile telephones. A recent standard is “Digital Video Broadcasting (DVB); Transmission System for Handheld Terminals (DVB-H)”, ETSI EN 302 304 V1.1.1 (June 2004). This is an extension of the current DVB-terrestrial (DVB-T) standard to support handheld devices and introduces a new transmission mode, IP datacasting (IPDC), which is described in “IPDC in DVB-H: Technical requirements”, DVB Project (June 2004). IPDC is the end-to-end DVB system, including a mobile interaction channel for mobile handheld broadcast services. See also “IP Datacast Baseline Specification; PSI/SI Guidelines for DVB-T/H Systems”, document A079, DVB Project (April 2004). For even more information, the interested reader is directed to http://www.dvb.org.
Moreover, inclusion of a separate DVB-H receiver in a user terminal also requires new terminal hardware and antennas. Different antennas might be needed in different countries due to spectrum allocations. Interoperability testing and verification due to new network nodes will delay introduction. Local distribution of programs/channels will be costly due to needed modifications of network structure, which is typically designed for national or regional coverage.
Compared with DVB-H and DVB-T, GERAN/UTRAN MBMS has a lower data rate. On the other hand, GERAN/UTRAN MBMS can transmit different information in each cell. Thus, GERAN/UTRAN MBMS is suitable for broadcasting content that is locally variable or broadcast/multicast-group dependent. UTRAN, or the UMTS Terrestrial Radio Access Network, is part of the Universal Mobile Telecommunication System (UMTS) and identifies the part of the network that includes radio network controllers (RNCs) and so-called Node Bs, which are analogous to base stations in other mobile telephone systems. UMTS is one of the third generation (3G) mobile telephone systems being developed within the IMT-2000 framework of the International Telecommunications Union (ITU) and standardized by the 3GPP.
Even so, to be competitive with DVB-H, the performance of cellular broadcast bearers can stand improvement. Dedicated unicast channels in either Enhanced GPRS (EGPRS) or WCDMA systems are difficult to use for mobile TV streaming because such channels will not scale to large usage. This problem of capacity limitations in the radio network is helped by MBMS, which provides one dedicated channel for each group of terminals receiving the same content. Nevertheless, a separate channel for a program guide or service description is also needed. Channel switching may also be slow with the currently standardized MBMS due to delays caused by restart of streaming sessions.